Whoa! This is huge. There are 65,536 possible graphs with 4 nodes,
and 33,554,432 possible graphs with 5 nodes.

If we think about the adjacency matrix representation of a graph,
there is an n × n matrix with a 0 or 1 in position [i][j]
iff there is an arc from i to j. Since there are n2
bits, the number of values of all possible matrices of bits is
2n2